Looking for advice about casting fundamentals

Affinity

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Your margins shouldnt face each other. Put a mark on the ring that will be the top of the mould when its in the cradle. Face the margins towards the trailing edge of the arm and slightly upward toward the top of the mould. Narrow your sprues where they connect so you dont get porosity. No offense but this is where our industry is going.. take the time to hand wax a crown and you will really care about how well it casts. Casting is not CAD/CAM, its what separates the men from the boys and it takes a while to get it figured out, hell im still learning too.
 
HonestAbe

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This was how in used to do things sprue wise. I'm not sure why the button at the end is so messed up and splashy it's usually a solid cone. I suspect I did not heat and melt the metal evenly?

20210924_103328.jpg

I also had this one get wayyyy bigger than I waxed and I'm not sure why please see other attachment
 

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HonestAbe

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Your margins shouldnt face each other. Put a mark on the ring that will be the top of the mould when its in the cradle. Face the margins towards the trailing edge of the arm and slightly upward toward the top of the mould. Narrow your sprues where they connect so you dont get porosity. No offense but this is where our industry is going.. take the time to hand wax a crown and you will really care about how well it casts. Casting is not CAD/CAM, its what separates the men from the boys and it takes a while to get it figured out, hell im still learning too.

This info about how to orient the crowns in the ring is one of the things I was searching for but I'm having a hard time visualizing it. My arm spins counter-clockwise so if I'm looking down at where I load the oval-shaped ring, all the margins in that ring should face to the right if I understand you correctly. I will be able to take a picture tomorrow and draw on it or something.

If I have this right in my head then all the crowns as I've been orienting them are 90 degrees rotated away from what's ideal, and since I haven't been paying attention to the "top" of the ring at all, the margins have been facing either up, or down in relation to the spin of the arm, and not left or right. Easy enough to rotate them but I can tell this is going to give me way less space in the oval ring.
 
Affinity

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Dont let your resevoirs touch each other keep them separate. Take a second to visualize which way the arm spins and let the margins face the other direction, the mark on the mould is to orient it after its invested and you cant see where they are. Also that casting you showed, doesnt have enough gold, there is no button, you should have a decent amount of gold there, which is why there is porosity in the resevoirs, which is better than in the crown but still looks like it didnt have enough gold to cast dense. make sure you weigh your patterns with the sprue and resevoir then add 5-10%. (.5g wax x 14 density= .7g alloy +.07g= around 8g total for .5g wax weight)
 
bigj1972

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Isn't anybody ready to say "I'm not paid enough for this sh*t!"
 
rkm rdt

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With the technology of scanners, design software and mills, I wouldn't go back to hand waxing a FGC unless something broke down. I may be nice to know how to do it, but let some of the tooth libraries, anatomy libraries do that work for you. I do re-seal in margin wax a bit if needed, or add to cusp tips, ridges etc. that I want to tweak. The only time I hand wax is if I'm running short on time for a PFM single, then it is faster for me to hand wax it. Otherwise, the CAD/CAM wax comes out so nice and clean and consistent.

By the way, I'm impressed with how attentive to this thread you've been, and so willing to learn. You've really gotten some wonderful advice here, right from the start of page 1 :)
Find a bot like CHL and pick his brain
 
Affinity

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Ive got a possible exit strategy too Gru, I think I can do another 5 years..
 
HonestAbe

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Dont let your resevoirs touch each other keep them separate. Take a second to visualize which way the arm spins and let the margins face the other direction, the mark on the mould is to orient it after its invested and you cant see where they are. Also that casting you showed, doesnt have enough gold, there is no button, you should have a decent amount of gold there, which is why there is porosity in the resevoirs, which is better than in the crown but still looks like it didnt have enough gold to cast dense. make sure you weigh your patterns with the sprue and resevoir then add 5-10%. (.5g wax x 14 density= .7g alloy +.07g= around 8g total for .5g wax weight)

Ah okay I think I got mixed up, thought someone said that the gold should just fill the reservoirs and a bit further, I'll include enough gold to get a decent button next cast. I've been sand blasting the button to make sure its very clean before I use it, but I've read that people grind the very end of it as well?
 
Affinity

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Sandblasting is fine, but make sure its clean, you dont need to grind it, it all melts the same. You want the gold to fill the resevoirs, but the button is the resevoir for the resevoirs..
 
HonestAbe

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We can just keep adding reservoirs until the porosity is so confused it gives up
 

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HonestAbe

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I have 4 crowns in the oven now, this time marked the top of the rings with margins facing trailing edge. Hoping it did it right but we shall see!

If some of my formers are leaking a little bit of investment after I set them aside to set (old and worn out I guess?) do I need to replace them or is there some trick to extending their life? Like a bit of wax to seal them better or something?
 
CatamountRob

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I just seal them with a bit of wax.
 
rkm rdt

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Any tips on casting from a boat CRob?
 
HonestAbe

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Finally got a chance to try Ron's sample wax puck (ty again Ron!). So far so good, the margins are definitely better than the other wax puck we had, and less fragile over all. Out of the 8 or so I've milled, one of them I had to cut away the margins and rewax them because they weren't quite good enough. The tech that does the metal finishing has only gotten her hands on a few after being cast so I'm still getting feedback about that, but casting another 4 today.

I'm doing everything with the margins facing the right way now, and that's been a nice improvement (thanks for the feedback there to everyone). I think I somehow messed up my math on the gold estimate last cast and barely had the reservoir filled but the crowns came out fine.

Since starting this thread and incorporating the advice given I've had zero porosity issues (knock on wood) and just an easier time getting things to go smoothly.
 
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